There is an increasing need for ruggedised racking for the installation of telecommunication equipment, e.g. switching equipment, in zones that are potentially subject to earthquake damage. These earthquake zones are classified according to the potential risk and the magnitude of earthquake damage, the most severe damage being expected in zone 4. There is a requirement that, in the event of an earthquake, the equipment supported in the rack will be protected from damage so that a communication service can be maintained without interruption. To meet this objective, an equipment rack must provide effective damping of the earthquake induced vibrations so as to minimise the forces that are transferred to the equipment mounted in the rack. The requirements for earthquake resistance are described in a test procedure detailed in the Bellcore NEBS standard entitled GR-63-CORE, Network Equipment Building System (NEBS) which recommends applied forces and wave forms which the rack should be able to resist.
One approach to this problem is described in specification number U.S. Pat. No. 5,004,107 which describes a rack in which the base portion is reinforced with metal gussets to provide a strong box-like structure which braces the rack against applied forces. While this provides an effective rugged structure which is resistant to applied forces resulting from an earthquake, the box-like base section occupies a significant proportion of the rack volume and limits the quantity of equipment that can be supported on the rack. Thus a larger number of racks are required to house a given volume of equipment than would be the case with conventional racking systems. This can limit the use of such a rack in confined situations where space is at a premium.
The object of the invention is to minimise or to overcome this disadvantage.
It is a further object of the invention to provide an improved earthquake resistant rack construction.